Method for generating reference signal sequence in multi-antenna wireless communication system and apparatus for same

ABSTRACT

The present application discloses a method in which a base station transmits a reference signal sequence in a wireless communication system. In detail, the method comprises the steps of: generating a pseudo-random sequence using a first m-sequence and a second m-sequence; generating the reference signal sequence using the pseudo-random sequence; and transmitting the reference signal to a mobile station via antenna ports different from one another. The second m-sequence has an initial value containing parameters for discriminating reference signal sequences among users.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/028,352, filed on Sep. 16, 2013, now U.S. Pat. No. 9,160,429, whichis a continuation of U.S. patent application Ser. No. 13/265,515, filedon Oct. 20, 2011, now U.S. Pat. No. 8,565,268, which is the NationalStage filing under 35 U.S.C. 371 of International Application No.PCT/KR2010/002710, filed on Apr. 29, 2010, which claims the benefit ofearlier filing date and right of priority to Korean Patent ApplicationNo. 10-2010-0039486, filed on Apr. 28, 2010, and also claims the benefitof U.S. Provisional Application No. 61/173,950, filed on Apr. 29, 2009,the contents of which are all incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of generating a reference signal sequencein a multi-antenna wireless communication system and apparatus therefor.

BACKGROUND ART

Generally, MIMO (multi-input multi-output) is a method that uses aplurality of transmitting antennas and a plurality of receivingantennas. And, this method may be able to improve efficiency intransceiving data. In particular, a transmitting or receiving stage of awireless communication system uses a plurality of antennas to increasecapacity or enhance performance. In the following description, the MIMOmay be called multiple antennas.

The MIMO technique does not depend on a single antenna path to receiveone whole message. Instead, the MIMO technique completes data by puttingfragments received via several antennas together. If the MIMO techniqueis adopted, a data transmission rate within a cell area having aspecific size may be improved or a system coverage may be increased bysecuring a specific data transmission rate. Moreover, this technique maybe widely applicable to a mobile communication terminal, a relay and thelike. According to the MIMO technique, it may be able to overcome thetransmission size limit of the related art mobile communication whichused to use a single data.

FIG. 1 is a diagram for a configuration of a general MIMO communicationsystem. N_(T) transmitting antennas are provided to a transmittingstage, while N_(R) receiving antennas are provided to a receiving stage.In case that each of the transmitting and receiving stages uses aplurality of antennas, theoretical channel transmission capacity isincreased more than that of a case that either the transmitting stage orthe receiving stage uses a plurality of antennas. The increase of thechannel transmission capacity is in proportion to the number ofantennas. Hence, a transmission rate is enhanced and frequencyefficiency can be raised. Assuming that a maximum transmission rate incase of using a single antenna is set to R₀, the transmission rate incase of using multiple antennas may be theoretically raised by a resultfrom multiplying the maximum transmission rate R₀ by a rate increasingrate R_(i), as shown in Formula 1. In this case, R_(i) is a smaller oneof N_(T) and N_(R).R _(i)=min(N _(T) ,N _(R))  [Formula 1]

For instance, in an MIMO communication system, which uses 4 transmittingantennas and 4 receiving antennas, it may be able to obtain atransmission rate 4 times higher than that of a single antenna system.After this theoretical capacity increase of the MIMO system has beenproved in the middle of 90's, many ongoing efforts are made to varioustechniques to substantially improve a data transmission rate. And,theses techniques are already adopted in part as standards for the 3Gmobile communications and various wireless communications such as a nextgeneration wireless LAN and the like.

The trends for the MIMO relevant studies are explained as follows. Firstof all, many ongoing efforts are made in various aspects to develop andresearch information theory study relevant to MIMO communicationcapacity calculations and the like in various channel configurations andmultiple access environments, radio channel measurement and modelderivation study for MIMO systems, spatiotemporal signal processingtechnique study for transmission reliability enhancement andtransmission rate improvement and the like.

In order to explain a communicating method in an MIMO system in detail,mathematical modeling can be represented as follows. Referring to FIG.1, assume that N_(T) transmitting antennas and N_(R) receiving antennasexist. First of all, regarding a transmission signal, if there are N_(T)transmitting antennas, N_(T) maximum transmittable informations exist.Hence, the transmission information may be represented by the vectorshown in Formula 2.s=[s ₁ ,s ₂ , . . . ,s _(N) _(T) ]^(T)  [Formula 2]

Meanwhile, transmission powers can be set different from each other fortransmission informations s₁, s₂, . . . , s_(N) _(T) , respectively. Ifthe transmission powers are set to P₁, P₂, . . . , P_(N) _(T) ,respectively, the transmission power adjusted transmission informationcan be represented as Formula 3.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Formula 3]

And, Ŝ may be represented as Formula 4 using a diagonal matrix P of thetransmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Let us consider a case of configuring N_(T) transmitted signals x₁, x₂,. . . , x_(N) _(T) , which are actually transmitted, by applying aweight matrix W to a transmission power adjusted information vector Ŝ.In this case, the weight matrix plays a role in properly distributingeach transmission information to each antenna according to atransmission channel status and the like. The transmitted signals areset to may x₁, x₂, . . . , x_(N) _(T) may be represented as Formula 5using a vector X. In this case, W_(ij) means a weight between an i^(th)transmitting antenna and a j^(th) information. And, the W may be calleda weight matrix or a precoding matrix.

$\begin{matrix}{x = {\quad{\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}\; N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\;\hat{s}} = {WPs}}}}}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Generally, a physical meaning of a rank of a channel matrix may indicatea maximum number for carrying different informations on a grantedchannel. Since a rank of a channel matrix is defined as a minimum numberof the numbers of independent rows or columns, a rank of a channel isnot greater than the number of rows or columns. For example by formula,a rank of a channel H (i.e., rank (H)) is limited by Formula 6.rank(H)≤min(N _(T) ,N _(R))  [Formula 6]

Meanwhile, each different information sent by MIMO technique may bedefined as ‘transport stream’ or ‘stream’ only. This ‘stream’ may becalled a layer. If so, the number of transport streams is unable to begreater than a channel rank, which is the maximum number for sendingdifferent informations. Hence, the channel matrix H may be representedas Formula 7.#of streams≤rank(H)≤min(N _(T) ,N _(R))  [Formula 7]

In this case, ‘# of streams’ may indicate the number of streams.Meanwhile, it should be noted that one stream is transmittable via atleast one antenna.

There may exist various methods for making at least one streamcorrespond to several antennas. This method may be described inaccordance with a type of MIMO technique as follows. First of all, ifone stream is transmitted via several antennas, it may be regarded asspatial diversity. If several streams are transmitted via severalantennas, it may be regarded as spatial multiplexing. Of curse, such anintermediate type between spatial diversity and spatial multiplexing asa hybrid type of spatial diversity and spatial multiplexing may bepossible.

DISCLOSURE OF THE INVENTION Technical Problem

Based on the above-mentioned discussion, a method for a base station totransmit a reference signal in a multi-antenna wireless communicationsystem and apparatus therefor may be proposed in the followingdescription.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method oftransmitting a reference signal sequence, which is transmitted by a basestation in a wireless communication system, according to the presentinvention may include the steps of generating a pseudo-random sequenceusing a first m-sequence and a second m-sequence, generating thereference signal sequence using the pseudo-random sequence, andtransmitting the reference signal to a mobile station via antenna portsdifferent from one another, wherein the second m-sequence has an initialvalue containing a parameter for discriminating an inter-user referencesignal sequence.

Preferably, the second m-sequence x₂(n) is determined byx₂(n+31)=(x₂(n+3)+x₂(n+2)+x₂(n+1)+x₂(n))mod 2 and the initial value ofthe second m-sequence is defined by c_(init)=Σ_(i=0) ³⁰x₂(i)·2^(i). Inparticular, the c_(init) is k+(└n_(s)/2┘+1)·(2N_(ID) ^(cell)+1)·2¹⁶(where the n_(s) indicates a slot number in a radio frame, the N_(ID)^(cell) indicates a cell ID, and the k indicates the parameter fordiscriminating the inter-user reference signal sequence).

More preferably, the parameter k for discriminating the inter-userreference signal sequence is signaled to the mobile station via adownlink physical control channel. And, the parameter k fordiscriminating the inter-user reference signal sequence may have a valueset to 0 or 1.

Meanwhile, if the base station operates in CoMP (coordinated multipoint) mode, the N_(ID) ^(cell) of the c_(init) is an ID (N_(ID)^(serving cell)) of a serving cell or an ID (N_(ID) ^(MU)) of a mobilestation group.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, abase station in a wireless communication system according to anotherembodiment of the present invention may include a processor generating apseudo-random sequence using a first m-sequence and a second m-sequence,the processor generating a reference signal sequence using thepseudo-random sequence and a transmitting module transmitting thereference signal to a mobile station via antenna ports different fromone another, wherein the second m-sequence has an initial valuecontaining a parameter for discriminating an inter-user reference signalsequence.

Advantageous Effects

According to an embodiment of the present invention, a mobile stationmay be able to effectively transmit a signal to a base station in amulti-antenna wireless communication system.

Effects obtainable from the present invention may be non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for a configuration of a general multi-antenna(MIMO) communication system.

FIG. 2 is a diagram of structures of control and user planes of a radiointerface protocol between a user equipment and E-UTRAN based on 3GPPradio access network specification.

FIG. 3 is a diagram for explaining physical channels used for 3GPPsystem and a general method of transmitting a signal using the same.

FIG. 4 is a diagram for an example of a structure of a radio frame usedfor LTE system.

FIG. 5 is a diagram for an example of a structure of a downlink (DL)radio frame used for LTE system.

FIG. 6 is a diagram for an example of a control channel included in acontrol region of one subframe in a DL radio frame.

FIG. 7 is a conceptional diagram for CoMP (coordinated multi-point)scheme of an intra base station (intra eNB) and an inter base station(inter eNB) according to a related art.

FIG. 8 is a diagram for a structure of a reference signal in LTE systemsupportive of DL transmission using 4 antennas.

FIG. 9 is an exemplary block diagram of a user equipment according toone embodiment of the present invention.

BEST MODE FOR INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The embodiments described in the following description mayinclude the examples showing that the technical features of the presentinvention are applied to 3GPP system.

Although an embodiment of the present invention is exemplarily describedin the present specification using the LTE system and the LTE-A system,the embodiment of the present invention may be also applicable to anykinds of communication systems corresponding to the above definitions.Although an embodiment of the present invention is exemplarily describedwith reference to FDD scheme in the present specification, theembodiment of the present invention is easily modifiable and applicableto H-FDD or TDD scheme.

FIG. 2 is a diagram of structures of control and user planes of a radiointerface protocol between a user equipment and E-UTRAN based on 3GPPradio access network specification. Especially, FIG. 2(a) is a diagramof structures of control plane of the radio interface protocol, and FIG.2(b) is a diagram of structures of user plane of the radio interfaceprotocol. First of all, a control plane may mean a passage fortransmitting control messages used by a user equipment and a network tomange a call. And, a user plane may mean a passage for transmitting suchdata generated from an application layer as voice data, internet packetdata and the like.

A physical layer, i.e., a first layer, provides an information transferservice to an upper layer using a physical channel. The physical layeris connected to a medium access control layer located above via atransport channel. Data are transferred between the medium accesscontrol layer and the physical layer via the transport channel. Data aretransferred between a physical layer of a transmitting side and aphysical layer of a receiving side via a physical channel. The physicalchannel uses time and frequency as radio resources. In particular, aphysical layer is modulated in downlink by OFDMA (orthogonal frequencydivision multiple access) scheme and is modulated in uplink by SC-FDMA(single carrier frequency division multiple access) scheme.

A medium access control (hereinafter abbreviated MAC) layer of a secondlayer provides a service to a radio link control (hereinafterabbreviated RLC) layer of an upper layer via a logical channel. The RLClayer o the second layer supports reliable data transfer. A function ofthe RLC layer can be implemented using a function block within the MAC.A packet data convergence protocol (hereinafter abbreviated PDCP) layerof the second layer performs a header compression function for reducingunnecessary control information to transmit such an IP packet as IPv4and IPv6 in a radio interface having a narrow bandwidth.

A radio resource control (hereinafter abbreviated RRC) layer located ona lowest level of a third layer is defined in a control plane only. TheRRC layer is responsible for controlling logical channel, transportchannel and physical channels in association with configuration,reconfiguration and release of radio bearers (RBs). In this case, the RBmeans a service provided by the second layer for a data transfer betweena user equipment and a network. For this, the RRC layer of the userequipment exchanges RRC messages with the RRC layer of the network. Ifthere is an RRC connection established between RRC layers of the userequipment and the network, the user equipment may be in a connectedmode. Otherwise, the user equipment may be in an RRC idle mode. NAS(non-access stratum) layer above the RRC layer may perform such afunction as session management, mobility management and the like.

One cell, which constructs a base station (eNB), is set to one ofbandwidths including 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHzand the like and may then provide an uplink or downlink transmissionservice to a plurality of user equipments. Different cells can be set toprovide different bandwidths, respectively.

A downlink transport channel for transporting data to a user equipmentfrom a network may include one of a broadcast channel (BCH) fortransporting system information, a paging channel (PCH) for transmittinga paging message, a downlink shared channel (SCH) for transmitting auser traffic or a control message and the like. A traffic or controlmessage of a downlink multicast or broadcast service can be transmittedvia a downlink SCH or a separate downlink multicast channel (MCH).Meanwhile, an uplink transport channel for transmitting data from a userequipment to a network may include one of a random access channel (RACH)for transmitting an initial control message, an uplink shared channel(SCH) for transmitting a user traffic or a control message or the like.A logical channel located above a transport channel to be mapped by atransport channel may include one of BCCH (Broadcast Control Channel),PCCH (Paging Control Channel), CCCH (Common Control Channel), MCCH(Multicast Control Channel), MTCH (Multicast Traffic Channel) and thelike.

FIG. 3 is a diagram for explaining physical channels used for 3GPPsystem and a general method of transmitting a signal using the same.

If a power of a user equipment is turned on or the user equipment entersa new cell, the user equipment may perform an initial cell search formatching synchronization with a base station and the like [S301]. Forthis, the user equipment receives a primary synchronization channel(P-SCH) and a secondary synchronization channel (S-SCH) from the basestation, matches synchronization with the base station and then obtainsinformation such as a cell ID and the like. Subsequently, the userequipment receives a physical broadcast channel from the base stationand is then able to obtain intra-cell broadcast information. Meanwhile,the user equipment may receive a downlink reference signal (DL RS) inthe initial cell searching step and may be then able to check a downlinkchannel status.

Having completed the initial cell search, the user equipment may receivea physical downlink control channel (PDCCH) and a physical downlinkshared control channel (PDSCH) according to information carried on thephysical downlink control channel (PDCCH) and may be then able to obtainsystem information in further detail [S302].

Meanwhile, if the user equipment initially accesses the base station orfails to have a radio resource for signal transmission, the userequipment may be able to perform a random access procedure (RACH) on thebase station [S303 to S306]. For this, the user equipment may transmit aspecific sequence as a preamble via a physical random access channel(PRACH) [S303, S305] and may be then able to receive a response messagevia PDCCH and a corresponding PDSCH in response to the preamble [S304,S306]. In case of contention based RACH, it may be able to perform acontention resolution procedure in addition.

Having performed the above mentioned procedures, the user equipment maybe able to perform PDCCH/PDSCH reception [S307] and PUSCH/PUCCH(physical uplink shared channel/physical uplink control channel)transmission [S308] as a general uplink/downlink signal transmissionprocedure. Meanwhile, control information transmitted/received inuplink/downlink to/from the base station by the user equipment mayinclude DL/UL ACK/NACK signal, CQI (channel quality indicator), PMI(precoding matrix index), RI (rank indicator) and the like. In case ofthe 3GPP LTE system, the user equipment may be able to transmit theabove-mentioned control information such as CQI, PMI, RI and the likevia PUSCH and/or PUCCH.

FIG. 4 is a diagram for an example of a structure of a radio frame usedfor LTE system.

Referring to FIG. 4, a radio frame has a length of 10 ms (327200·T_(s))and is constructed with 10 subframes in equal size. Each of thesubframes has a length of 1 ms and is constructed with two slots. Eachof the slots has a length of 0.5 ms (15360 T_(s)). In this case, T_(s)indicates a sampling time and is expressed as T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (about 33 ns). The slot includes a plurality ofOFDM symbols in a time domain and includes a plurality of resourceblocks (RB) in a frequency domain. In the LTE system, one resource blockincludes ‘12 subcarriers×7 or 6 OFDM symbols’. A transmission timeinterval (TTI), which is a unit time for transmitting data, can bedetermined by at least one subframe unit. The above described structureof the radio frame is just exemplary. And, the number of subframesincluded in a radio frame, the number of slots included in a subframeand/or the number of OFDM symbols included in a slot may be modified invarious ways.

FIG. 5 is a diagram for an example of a structure of a downlink (DL)radio frame used for LTE system.

Referring to FIG. 5, a DL radio frame may include 10 subframes equal toeach other in size. A subframe in 3GPP LTE system may be defined by abasic time unit of packet scheduling for all DL link frequency. Eachsubframe may be divided into a time interval (i.e., control region) fortransmission of scheduling information and other control informationsand a time interval (i.e., data region) for DL data transmission. Thecontrol region starts with a 1^(st) OFDM symbol and may include at leastone or more OFDM symbols. A size of the control region may be setindependent per subframe. The control region may be used to transmitL1/L2 (layer 1/layer 2) control signal. And, the data region may be usedto transmit DL traffic.

FIG. 6 is a diagram for an example of a control channel included in acontrol region of one subframe in a DL radio frame.

Referring to FIG. 6, a subframe may include 14 OFDM symbols. First 1 to3 OFDM symbols may be used as a control region and the rest of 13 to 11OFDM symbols may be used as a data region, in accordance with subframesettings. In the drawing, R1 to R4 indicate reference signals (RS) orpilot signals for antennas 0 to 3, respectively. The RS may be fixed toa predetermined pattern in a subframe irrespective of the control regionor the data region. The control region may be assigned to a resource, towhich the RS is not assigned, in the control region. And, a trafficchannel may be assigned to a resource, to which the RS is not assigned,in the data region. Control channels assigned to the control region mayinclude PCFICH (Physical Control Format Indicator CHannel), PHICH(Physical Hybrid-ARQ Indicator CHannel), PDCCH (Physical DownlinkControl CHannel) and the like.

FIG. 7 is a conceptional diagram for CoMP (coordinated multi-point)scheme of an intra eNB and an inter eNB according to a related art.

Referring to FIG. 7, intra base stations 710 and 720 and an inter basestation 730 exist in a multi-cell environment. In LTE (long termevolution) system, an intra base station is constructed with severalcells (or sectors). Cells belonging to a base station having a specificuser equipment belong thereto have relation as the intra base stations710 and 720 with the specific user equipment. In particular, cellsbelonging to the same base station of the cell having a user equipmentbelong thereto are the cells corresponding to the intra base stations710 and 720. And, cells belonging to other base stations become thecells corresponding to the inter base station 730.

Thus, cells based on the same base station of a specific user equipmentare physically co-located, they may share information (e.g., data,channel state information (CSI), etc.) with each other. Yet, cells basedon another base station may be able to exchange inter-cell informationvia a backhaul 740 and the like. Referring to FIG. 7, a single cell MIMOuser 750 within a single cell may communicate with one serving basestation in one cell (or sector). A multi-cell MIMO user 760 located on acell boundary may be able to communicate with a plurality of servingbase stations in a multi-cell (or multi-sector).

Coordinated multi-point (CoMP) scheme (hereinafter abbreviated CoMPscheme) may include the system to improve throughput of a user locatedon a cell boundary by applying enhanced MIMO transmission in amulti-cell environment. If the CoMP scheme is applied, it may be able toreduce inter-cell interference in the multi-cell environment. If theCoMP scheme is used, a mobile station may be provided with a supportfrom multi-cell base stations jointly. Moreover, each base station maybe able to enhance system performance by supporting at least one or moremobile stations MS1, MS2, . . . MSK simultaneously using the same radiofrequency resource. Moreover, the base station may be able to performspace division multiple access (SDMA) method based on state informationof a channel between the base station and the mobile station. Operatingmodes of the CoMP scheme can be categorized into a joint processing modeof a coordinated MIMO type through data sharing and a CS/CB (coordinatedscheduling/coordinated beamforming) mode.

In a wireless communication system having the CoMP scheme appliedthereto, a serving base station and at least one or more coordinatedbase stations may be connected to a scheduler via a backbone network.The scheduler may be able to operate by receiving feedback of channelinformation on a channel state between each of the mobile stations (MS1,MS2, . . . MSK) and the coordinated base station. For instance, thescheduler may schedule information for a coordinated MIMO operation forthe serving base station and the at least one coordinated base station.In particular, the scheduler may directly instruct each base station ofthe coordinated MIMO operation.

In the following description, the reference signal may be explained indetail. Generally, for the channel measurement, a reference signalalready known to both a transmitting side and a receiving side istransmitted to the receiving side by the transmitting side. Thisreference signal indicates a modulation scheme as well as the channelmeasurement to play a role in activating a demodulating process. And,reference signals may be classified into a dedicated RS (DRS) for a basestation and a specific mobile station and a common RS (CRS) for allmobile stations.

FIG. 8 is a diagram for a structure of a reference signal in LTE systemsupportive of DL transmission using 4 antennas. Particularly, FIG. 8 (a)shows a case of a normal cyclic prefix and FIG. 8 (b) shows a case of anextended cyclic prefix.

Referring to FIGS. 8, 0 to 3 written in lattices may mean cell-specificCRS transmitted for channel measurement and data demodulation in amanner of corresponding to ports 0 to 3, respectively. ‘D’ written in alattice may mean a UE-specific RS which is a dedicated RS and maysupport a single antenna port transmission via a data region, i.e.,PDSCH. A user equipment receives signaling for a presence ornon-presence of the UE-specific RS via an upper layer.

In a related art LTE system, for the scrambling of a reference signaland a physical channel, the reference signal us generated using apseudo-random sequence c(n). The pseudo-random sequence c(n) may bedefined as Formula 8 using a gold sequence having a length 31.c(n)=(x ₁ n+N _(C))+x ₂(n+N))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2  [Formula 8]

In Formula 8, N_(C) is 1600 and a 1^(st) m-sequence has an initial valueof x₁(0) set to 1 and x₁(n) set to 0 (yet, n is 1˜30). An initial valueof a 2^(nd) m-sequence is defined as c_(init)=Σ_(i=0) ³⁰x₂(i)·2^(i) andits value may be determined in accordance with a usage of thecorresponding sequence.

In a cell-specific reference signal, the emit may be defined as Formula9 and may be initialized for each OFDM symbol.c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(cell)+1)+2·N _(ID) ^(cell)+N _(CP)  [Formula 9]

In Formula 9, the n_(s) indicates a slot number in a radio frame and theN_(ID) ^(cell) indicates a cell ID. The N_(CP) has a value of 1 for anormal CP and has a value of 0 for an extended CP.

In MBSFN reference signal, the c_(init) may be defined as Formula 1.And, In the MBSFN reference signal, the c_(init) may be initialized foreach OFDM symbol.c _(init)=2⁹·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(MBSFN)+1)=N _(ID)^(MBSFN)  [Formula 10]

In Formula 10, the N_(ID) ^(MBSFN) may be signaled to a user equipmentvia an upper layer.

Finally, in a UE-specific reference signal, the c_(init) may be definedas Formula 11 and may be initialized at a start point of a subframe.c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +n _(RNTI)  [Formula11]

In Formula 11, the n_(RNTI) may specifically have a different valueaccording to an application. In particular, SPS-RNTI is used for asemi-persistent transmission) or C-RNTI may be used for anon-semi-persistent transmission.

Meanwhile, DM-RS may be a reference signal used to decode data receivedby a user equipment from a base station. The base station transmits theDM-RS by applying the same matrix applied to data. Therefore, the DM-RSis a UE-specific reference signal and may be generated using apseudo-random sequence c(n) as show in Formula 12.

$\begin{matrix}{{{r_{n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\;\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},\mspace{20mu}{m = 0},1,\ldots\mspace{14mu},{{12N_{RB}^{PDSCH}} - 1}} & \left\lbrack {{Formula}\mspace{14mu} 12} \right\rbrack\end{matrix}$

A reference signal sequence shown in Formula 12 may be applicable to asingle-cell single-user MIMO transmission, a single-cell multi-user MIMOtransmission, a multi-cell single-user MIMO transmission and amulti-cell multi-user MIMO transmission all.

The present invention may propose that the initial value c_(init) of the2^(nd) m-sequence used for the pseudo-random sequence generation inFormula 12 is separately defined to be applicable to MIMO transmissionmodes. In particular, as shown in Formula 11, the c_(init) proposed bythe present invention may be characterized in having factors set toN_(ID) ^(cell) and n_(RNTI) and further including a scramblediscriminating parameter N_(DRS) as a factor.

In this case, if a cell-specific reference signal and a DM-RS co-existin the same OFDM symbol, the N_(DRS) may be set to a value of 1.Otherwise, the N_(DRS) may be set to a value of 0. And, the N_(DRS) maybe separately signaled from a base station via DCI format 2B received onPDCCH. Moreover, the N_(ID) ^(cell) may mean a cell ID or a group ID ofa user group in a multi-cell multi-user MIMO mode.

Finally, regarding n_(RNTI), SPS-RNTI may be used for semi-persistenttransmission or C-RNTI may be usable for a non-semi-persistenttransmission. Yet, the n_(RNTI) may be set to 0 in accordance with amultiplexing scheme of DM-RS.

In LTE system, when there are 2 antenna ports for DM-RS transmission, ifa multiplexing scheme is frequency division multiplexing, c_(init) maybe defined as Formula 13.c _(init) =N _(DRS)2³⁰=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ n_(RNTI)  [Formula 13]

Moreover, regarding the c_(init) for supporting a single-cell multi-userMIMO mode transmission, if a multiplexing scheme for an antenna port isfrequency division multiplexing, the n_(RNTI) may be set to 0 to definethe c_(init).c _(init) =N _(DRS)2³⁰+(└n _(s)/2┘+1)·(2N _(ID) ^(cell)=1)·2¹⁶  [Formula14]c _(init) =N _(DRS)2¹⁴+(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1).  [Formula15]c _(init) =N _(DRS)+(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶  [Formula16]

In the CoMP scheme, it may be preferable that the N_(ID) ^(cell) is setto indicate a serving cell ID for CoMP transmission. Hence, Formula 12may be modified into Formula 17.c _(init) =N _(DRS)2³⁰+(└n _(s)/2┘+1)·(2N _(ID) ^(serving cell)+1)·2¹⁶+n _(RNTI)  [Formula 17]

Likewise, if a multiplexing scheme for an antenna port is frequencydivision multiplexing, the n_(RNTI) may be set to 0 to define thec_(init) as Formulas 18 to 20.c _(init) =N _(DRS)2³⁰+(└n _(s)/2┘+1)·(2N _(ID)^(serving cell)+1)·2¹⁶  [Formula 18]c _(init) =N _(DRS)2¹⁴+(└n _(s)/2┘+1)·(2N _(ID)^(serving cell)+1)  [Formula 19]c _(init) =N _(DRS)+(└n _(s)/2┘+1)·(2N _(ID)^(serving cell)+1)·2¹⁶  [Formula 20]

For a multi-cell multi-user MIMO transmission in the CoMP scheme, theN_(ID) ^(cell) is set to N_(ID) ^(MU) indicating a serving cell ID ofCoMP transmission or an ID of a UE group to define the emit as Formula21 to 23.c _(init) =N _(DRS)2³⁰+(└n _(s)/2┘+1)·(2N _(ID) ^(MU)+1)·2¹⁶  [Formula21]c _(init) =N _(DRS)2¹⁴+(└n _(s)/2┘+1)·(2N _(ID) ^(MU)+1)  [Formula 22]c _(init) =N _(DRS)+(└n _(s)/2┘+1)·(2N _(ID) ^(MU)+1)·2¹⁶  [Formula 23]

Particularly, in Formulas 21 to 23, if the N_(ID) ^(MU) is an ID of aserving cell, a reference signal may be set as a cell-specific referencesignal. If the N_(ID) ^(MU) is an ID of a UE group, a reference signalmay be set as a UE-specific reference signal.

FIG. 9 is an exemplary block diagram of a user equipment according toone embodiment of the present invention.

Referring to FIG. 9, a user equipment 900 may include a processor 910, amemory 920, an RF module 930, a display module 940 and a user interfacemodule 950.

The user equipment 900 is illustrated for clarity and convenience of thedescription and some modules thereof may be omitted. Moreover, the userequipment 900 may be able to further include at least one necessarymodule. And, some modules of the user equipment 900 may be furtherdivided into sub-modules. The processor 910 may be configured to performoperations according to the embodiment of the present inventionexemplarily described with reference to the accompanying drawings.

In particular, the processor 190 may perform operations required formultiplexing a control signal and a data signal. And, the detailedoperations of the processor 910 may refer to the contents described withreference to FIGS. 1 to 8.

The memory 920 may be connected to the processor 910 and may storeoperating systems, applications, program codes, data and the like. TheRF module 930 may be connected to the processor 910 and may perform afunction of converting a baseband signal to a radio signal or a functionof converting a radio signal to a baseband signal. For this, the RFmodule 930 may perform analog conversion, amplification, filtering andfrequency uplink transform or inverse processes thereof. The displaymodule 940 may be connected to the processor 910 and may display variouskinds of informations. The display module 940 may include such awell-known component as LCD (Liquid Crystal Display), LED (LightEmitting Diode), OLED (Organic Light Emitting Diode) and the like, bywhich the present invention may be non-limited. The user interfacemodule 950 may be connected to the processor 910 and may include acombination of well-known interfaces including a keypad, a touchscreenand the like.

The above described embodiments correspond to combination of elementsand features of the present invention in prescribed forms. And, it isable to consider that the respective elements or features are selectiveunless they are explicitly mentioned. Each of the elements or featurescan be implemented in a form failing to be combined with other elementsor features. Moreover, it is able to implement an embodiment of thepresent invention by combining elements and/or features together inpart. A sequence of operations explained for each embodiment of thepresent invention can be modified. Some configurations or features ofone embodiment can be included in another embodiment or can besubstituted for corresponding configurations or features of anotherembodiment. It is apparent that an embodiment can be configured bycombining claims, which are not explicitly cited in-between, togetherwithout departing from the spirit and scope of ‘what is claimed is’ orthat those claims can be included as new claims by revision after filingan application.

In the present disclosure, embodiments of the present invention may bedescribed centering on the data transmission/reception relations betweena relay node and a base station. In this disclosure, a specificoperation explained as performed by a base station may be performed byan upper node of the base station in some cases. In particular, in anetwork constructed with a plurality of network nodes including a basestation, it is apparent that various operations performed forcommunication with a terminal can be performed by a base station orother network nodes except the base station. In this case, ‘basestation’ may be replaced by such a terminology as a fixed station, aNode B, an eNode B (eNB), an access point and the like. And, a terminalmay be replaced by such a terminology as UE (User Equipment), MS (MobileStation), MSS (Mobile Subscriber Station) and the like.

Embodiments of the present invention may be implemented using variousmeans. For instance, embodiments of the present invention can beimplemented using hardware, firmware, software and/or any combinationsthereof. In case of the implementation by hardware, one embodiment ofthe present invention may be implemented by at least one selected fromthe group consisting of ASICs (application specific integratedcircuits), DSPs (digital signal processors), DSPDs (digital signalprocessing devices), PLDs (programmable logic devices), FPGAs (fieldprogrammable gate arrays), processor, controller, microcontroller,microprocessor and the like.

In case of the implementation by firmware or software, one embodiment ofthe present invention may be implemented by modules, procedures, and/orfunctions for performing the above-explained functions or operations.Software code may be stored in a memory unit and may be then drivable bya processor. The memory unit may be provided within or outside theprocessor to exchange data with the processor through the various meansknown to the public.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

As mentioned in the foregoing description, although a method ofgenerating a reference signal sequence in a multi-antenna wirelesscommunication system and apparatus therefor are described mainly withreference to examples applied to 3GPP LTE system, the present inventionmay be applicable to various kinds of multi-antenna wirelesscommunication systems as well as the 3GPP LTE system.

What is claimed is:
 1. A method of transmitting a user equipment (UE)specific reference signal sequence by a base station (BS) in a wirelesscommunication system, the method comprising: generating the UE specificreference signal sequence based on a pseudo-random sequence defined by afirst m-sequence and a second m-sequence; transmitting the UE specificreference signal sequence to a UE, wherein an initial value of the firstm-sequence is a fixed value, wherein an initial value of the secondm-sequence is determined using a cell identity, wherein the cellidentity is configured based on a transmission mode of the BS, whereinthe pseudo-random sequence is represented as c(n) and is defined byfollowing equation A:c(n)=(x ₁ n+N _(C))+x ₂(n+N _(C)))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2,  [Equation A] whereN_(C)=1600, wherein the first m-sequence is represented as x₁(n) and isinitialized with x₁(0)=1, x₁(n)=0, n=1, 2, . . . , 30, and wherein thesecond m-sequence is represented as x₂(n), and wherein an initial valueof the second m-sequence is represented by(└n _(s)/2┘+1)·(2n _(ID)+1)·2¹⁶ +k, wherein k is an indicator indicatedby a physical downlink control channel (PDCCH), where n_(s) is a slotnumber within a radio frame and n_(ID) is the cell identity.
 2. Themethod of claim 1, wherein the UE specific reference signal sequence isrepresented as r(m) and is defined by following equation B:$\begin{matrix}{{{r(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\;\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},\mspace{20mu}{m = 0},1,\ldots\mspace{14mu},{{12\; N_{RB}^{PDSCH}} - 1},} & \left\langle {{equation}\mspace{14mu} B} \right\rangle\end{matrix}$ where N_(RB) ^(PDSCH) is a number of resource blocksallocated to a Physical downlink shared channel (PDSCH).
 3. A basestation (BS) in a wireless communication system, the BS comprising: aprocessor for generating a user equipment (UE) specific reference signalsequence based on a pseudo-random sequence defined by a first m-sequenceand a second m-sequence; and a Radio Frequency (RF) module fortransmitting the UE specific reference signal sequence to a UE, whereinan initial value of the first m-sequence is a fixed value, wherein aninitial value of the second m-sequence is determined using a cellidentity, wherein the cell identity is configured based on atransmission mode of the BS, wherein the pseudo-random sequence isrepresented as c(n) and is defined by following equation A:c(n)=(x ₁ n+N _(C))+x ₂(n+N _(C)))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2,  [Equation A] whereN_(C)=1600, wherein the first m-sequence is represented as x₁(n) and isinitialized with x₁(0)=1, x₁(n)=0, n=1, 2, . . . , 30, and wherein thesecond m-sequence is represented as x₂(n), and wherein an initial valueof the second m-sequence is represented by(└n _(s)/2┘+1)·(2n _(ID)+1)·2¹⁶ +k, wherein k is an indicator indicatedby a physical downlink control channel (PDCCH), where n_(s) is a slotnumber within a radio frame and n_(ID) is the cell identity.
 4. A methodfor receiving a user equipment (UE) specific reference signal sequenceat a UE in a wireless communication system, the method comprising:receiving the UE specific reference signal sequence from a base station(BS); and demodulating a Physical downlink shared channel (PDSCH) basedon the UE specific reference signal sequence, wherein the UE specificreference signal sequence is generated based on a pseudo-random sequencedefined by a first m-sequence and a second m-sequence, wherein aninitial value of the first m-sequence is a fixed value, wherein aninitial value of the second m-sequence is determined using a cellidentity, wherein the cell identity is configured based on atransmission mode of the BS, wherein the pseudo-random sequence isrepresented as c(n) and is defined by following equation A:c(n)=(x ₁ n+N _(C))+x ₂(n+N _(C)))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2,  [Equation A] whereN_(C)=1600, wherein the first m-sequence is represented as x₁(n) and isinitialized with x₁(0)=1, x₁(n)=0, n=1, 2, . . . , 30, and wherein thesecond m-sequence is represented as x₂(n), and wherein an initial valueof the second m-sequence is represented by(└n _(s)/2┘+1)·(2n _(ID)+1)·2¹⁶ +k, wherein k is an indicator indicatedby a physical downlink control channel (PDCCH), where n_(s) is a slotnumber within a radio frame and n_(ID) is the cell identity.
 5. Themethod according to claim 4, wherein the UE specific reference signalsequence is represented as r(m) and is defined by following equation B:$\begin{matrix}{{{r(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\;\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},\mspace{20mu}{m = 0},1,\ldots\mspace{14mu},{{12\; N_{RB}^{PDSCH}} - 1},} & \left\langle {{equation}\mspace{14mu} B} \right\rangle\end{matrix}$ where N_(RB) ^(PDSCH) is a number of resource blocksallocated to a Physical downlink shared channel (PDSCH).
 6. A userequipment (UE) in a wireless communication system, the UE comprising: aRadio Frequency (RF) module for receiving a UE specific reference signalsequence from a base station (BS); and a processor for demodulating aPhysical downlink shared channel (PDSCH) based on the UE specificreference signal sequence, wherein the UE specific reference signalsequence is generated based on a pseudo-random sequence defined by afirst m-sequence and a second m-sequence, wherein an initial value ofthe first m-sequence is a fixed value, wherein an initial value of thesecond m-sequence is determined using a cell identity, wherein the cellidentity is configured based on a transmission mode of the BS, whereinthe pseudo-random sequence is represented as c(n) and is defined byfollowing equation A:c(n)=(x ₁ n+N _(C))+x ₂(n+N _(C)))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2,  [Equation A] whereN_(C)=1600, wherein the first m-sequence is represented as x₁(n) and isinitialized with x₁(0)=1, x₁(n)=0, n=1, 2, . . . , 30, and wherein thesecond m-sequence is represented as x₂(n), and wherein an initial valueof the second m-sequence is represented by(└n _(s)/2┘+1)·(2n _(ID)+1)·2¹⁶ +k, wherein k is an indicator indicatedby a physical downlink control channel (PDCCH), where n_(s) is a slotnumber within a radio frame and n_(ID) is the cell identity.